help with X86 DAG->DAG Instruction Selection

I have an llvm ir, which generates the following machine code using llc (llvm 3.0 on win32) after # *** IR Dump After X86 DAG->DAG Instruction Selection ***:

The first three lines and the last two lines alone together are used to compute “sin” for some double number.

  • line 1: move the stack pointer down 8

  • line 2: copy the updated stack pointer to a base register

  • line 3: copy a double number to location pointed by the base register

  • line end-1: to the last call “sin” to compute the result

  • line end: move the stack pointer up 8

The problem is that there are many other instructions inserted between them, and these instructions include stack allocations. This causes:

  1. “sin” function gets the wrong value to compute because the stack pointer moves and wrong value is received.
  2. the function call after line end could get wrong values because after line end the stack pointer is pointing to useful data.

Could anyone working on x86 instruction selection give some pointers to prevent this?


ADJCALLSTACKDOWN32 8, %ESP<imp-def,dead>, %EFLAGS<imp-def,dead>, %ESP ; line 1
%vreg187 = COPY %ESP; GR32:%vreg187 ; line 2
MOVSDmr %vreg187, 1, %noreg, 0, %noreg, %vreg36; mem:ST8[Stack] GR32:%vreg187 FR64:%vreg36 ; line 3
%vreg188 = MOV32rm %vreg112, 1, %noreg, 252, %noreg; mem:LD4[%108] GR32:%vreg188,%vreg112
%vreg189 = MOV32rm %vreg112, 1, %noreg, 256, %noreg; mem:LD4[%111] GR32:%vreg189,%vreg112
%vreg190 = MOVSDrm <fi#0>, 1, %noreg, 120, %noreg; mem:LD8[%85] FR64:%vreg190
%vreg191 = MOVSDrm <fi#0>, 1, %noreg, 96, %noreg; mem:LD8[%87] FR64:%vreg191
%vreg192 = MOVSDrm <fi#0>, 1, %noreg, 88, %noreg; mem:LD8[%92] FR64:%vreg192
%vreg193 = MOVSDrm <fi#0>, 1, %noreg, 24, %noreg; mem:LD8[%89] FR64:%vreg193
%vreg194 = MOVSDrm <fi#0>, 1, %noreg, 80, %noreg; mem:LD8[%94] FR64:%vreg194
%vreg195 = MOV32ri 8; GR32:%vreg195
%EAX = COPY %vreg195; GR32:%vreg195
WIN_ALLOCA %EAX<imp-def,dead>, %ESP<imp-def,dead>, %EFLAGS<imp-def,dead>, %ESP
%vreg196 = COPY %ESP; GR32:%vreg196
MOV32mr %vreg196, 1, %noreg, 0, %noreg, %vreg16; mem:ST4[%114] GR32:%vreg196,%vreg16
%vreg197 = MOV32ri 72; GR32:%vreg197
%EAX = COPY %vreg197; GR32:%vreg197
WIN_ALLOCA %EAX<imp-def,dead>, %ESP<imp-def,dead>, %EFLAGS<imp-def,dead>, %ESP
%vreg198 = COPY %ESP; GR32:%vreg198
MOVSDmr %vreg198, 1, %noreg, 56, %noreg, %vreg194; mem:ST8[%116+56] GR32:%vreg198 FR64:%vreg194
MOVSDmr %vreg198, 1, %noreg, 64, %noreg, %vreg17; mem:ST8[%116+64] GR32:%vreg198 FR64:%vreg17
MOVSDmr %vreg198, 1, %noreg, 48, %noreg, %vreg192; mem:ST8[%116+48] GR32:%vreg198 FR64:%vreg192
MOVSDmr %vreg198, 1, %noreg, 32, %noreg, %vreg191; mem:ST8[%116+32] GR32:%vreg198 FR64:%vreg191
MOVSDmr %vreg198, 1, %noreg, 24, %noreg, %vreg36; mem:ST8[%116+24] GR32:%vreg198 FR64:%vreg36
MOVSDmr %vreg198, 1, %noreg, 16, %noreg, %vreg190; mem:ST8[%116+16] GR32:%vreg198 FR64:%vreg190
MOVSDmr %vreg198, 1, %noreg, 8, %noreg, %vreg190; mem:ST8[%116+8] GR32:%vreg198 FR64:%vreg190
MOVSDmr %vreg198, 1, %noreg, 0, %noreg, %vreg190; mem:ST8[%116] GR32:%vreg198 FR64:%vreg190
%vreg199 = MOVSDrm %noreg, 1, %noreg, <cp#4>, %noreg; mem:LD8ConstantPool FR64:%vreg199
%vreg200 = FsXORPDrr %vreg193, %vreg199; FR64:%vreg200,%vreg193,%vreg199
MOVSDmr %vreg198, 1, %noreg, 40, %noreg, %vreg200; mem:ST8[%116+40] GR32:%vreg198 FR64:%vreg200
%vreg201 = MOV32ri 16; GR32:%vreg201
%EAX = COPY %vreg201; GR32:%vreg201
WIN_ALLOCA %EAX<imp-def,dead>, %ESP<imp-def,dead>, %EFLAGS<imp-def,dead>, %ESP
%vreg202 = COPY %ESP; GR32:%vreg202
MOV32mr %vreg202, 1, %noreg, 8, %noreg, %vreg19; mem:ST4[%118+8] GR32:%vreg202,%vreg19
MOV32mr %vreg202, 1, %noreg, 4, %noreg, %vreg18; mem:ST4[%118+4] GR32:%vreg202,%vreg18
MOV32mr %vreg202, 1, %noreg, 0, %noreg, %vreg0; mem:ST4[%118] GR32:%vreg202,%vreg0
CALLpcrel32 es:sin, %EAX<imp-def,dead>, %EFLAGS<imp-def,dead>, %ESP, … ; line end-1
ADJCALLSTACKUP32 8, 0, %ESP<imp-def,dead>, %EFLAGS<imp-def,dead>, %ESP ; line end

Hi Peng,

Can you please open a bugzilla and attache the LL file ? Can you please reproduce it on ToT ?


Hi Nadav,

Bug is reported with test cases. see .

Please let me know if you have any thought on this.